The invention relates to variable reluctance electric motors and, particularly, to electric motors whose electrically-energized salient stator poles terminate in stator teeth that oppose rotor teeth on the rotor surface, and in which permanent magnets located between adjacent stator teeth and poled transverse to the stator-to-rotor gap enhance the motor torque relative to the applied excitation in ampere-turns.
Such electric motors are disclosed in the aforementioned U.S. applications Ser. No. 612,563 and Ser. No. 735,935. The enhancement disclosed in these applications affords hybrid stepping motors and variable reluctance motors substantial increases, such as 50%, in torque constant. Permanent magnets, of materials such as samarium cobalt are located between the stator teeth of hybrid stepping motors and between both the stator teeth and rotor teeth of variable reluctance motors. These magnets between stator teeth increase the utilization of the rotor's permanent magnet flux for a given ampere-turn excitation of the phase coils surrounding the stator poles. The "inter-teeth" magnets achieve this result by controlling the motor's working air gap and altering the permeance slope, i.e. the torque making mechanism. The inter-teeth magnets also increase the rate of change of flux through the teeth when the motor rotates, thereby improving the motor's performance as a generator.
However, using these techniques on past variable reluctance motors has required placing such magnets between the teeth on the periphery of the rotor. This increases the rotor's inertia. Also, it makes the motor difficult to manufacture and increases its weight and cost.